The instant invention relates composite hydrogen storage materials including 1) hydrogen storage materials and 2) additional catalytic materials. The catalytic materials of the instant invention are based on a disordered non-equilibrium material designed to have fast kinetics, high density of catalytically active sites, resistance to poisoning, and long operating life. The instant composite material is not only useful for hydrogen storage, but is also useful as the anode materials for fuel cells and more specifically to Ovonic instant startup fuel cells.
The instant application discloses hydrogen storage materials and fuel cells that overcome the major deterrents to the widespread utilization of such. Namely, the instant inventors have solved the major barriers present in modern hydrogen storage and fuel cell technology, using materials which contain no costly noble metals therein. These barriers include: hydrogen storage capabilities, requisite catalytic activity, ionic conductivity, corrosion resistance, and increased resistance toward the poisoning effect of different gases. Additionally these materials must be low cost, containing no noble metals, so that fuel cells can be widely utilized. The anodes that are present in the fuel cells have catalytic material and hydrogen storage material (allowing for instant startup) using active materials which contain no noble metals. The fuel cells are capable of instantaneous startup and can store recaptured energy from processes such as regenerative braking. The materials are robust and poison resistant. The electrodes are easy to produce, by proven low cost production techniques, such as those presently employed in the production of Ovonic Ni-MH batteries. Carbon is eliminated from the anode, where in the prior art it tends to be oxidized to carbon dioxide, thus helping to eliminating the carbonate poisoning of the fuel cell electrolyte. The hydrogen storage materials of the anode are dense enough to block carbon dioxide from entering the electrolyte via the hydrogen fuel stream, but allow hydrogen to pass, acting as a hydrogen pump. The instant fuel cells have increased efficiency and power availability (higher voltage and current) and a dramatic improvement in operating temperature range (from xe2x88x9220 to 150xc2x0 C.) The fuel cell system of the instant invention allows for widespread utilization of fuel cells in all sectors of the energy production/consumption market, thereby further fostering the realization of a hydrogen based economy. An infrastructure for such a hydrogen based economy is disclosed in U.S. application Ser. No. 09/444,810, entitled xe2x80x9cA Hydrogen-based Ecosystemxe2x80x9d filed on Nov. 22, 1999 for Ovshinsky, et al. (the ""810 application), which is hereby incorporated by reference. This infrastructure, in turn, is made possible by hydrogen storage alloys that have surmounted the chemical, physical, electronic and catalytic barriers that have heretofore been considered insoluble. These alloys are fully described in copending U.S. patent application Ser. No. 09/435,497, entitled xe2x80x9cHigh Storage Capacity Alloys Enabling a Hydrogen-based Ecosystemxe2x80x9d, filed on Nov. 6, 1999 for Ovshinsky et al. (the ""497 application), which is hereby incorporated by reference.
As the world""s population expands and its economy increases, the atmospheric concentrations of carbon dioxide are warming the earth causing climate change. However, the global energy system is moving steadily away from the carbon-rich fuels whose combustion produces the harmful gas. Experts say atmospheric levels of carbon dioxide may be double that of the pre-industrial era by the end of the next century, but they also say the levels would be much higher except for a trend toward lower-carbon fuels that has been going on for more than 100 years. Furthermore, fossil fuels cause pollution and are a causative factor in the strategic military struggles between nations. Furthermore, fluctuating energy costs are a source of economic instability worldwide
In the United States, it is estimated, that the trend toward lower-carbon fuels combined with greater energy efficiency has, since 1950, reduced by about half the amount of carbon spewed out for each unit of economic production. Thus, the decarbonization of the energy system is the single most important fact to emerge from the last 20 years of analysis of the system. It had been predicted that this evolution will produce a carbon-free energy system by the end of the 21st century. The present invention is another product which is essential to shortening that period to a matter of years. In the near term, hydrogen will be used in fuel cells for cars, trucks and industrial plants, just as it already provides power for orbiting spacecraft. But, with the problems of storage and infrastructure solved (see the ""810 and ""497 applications), hydrogen will also provide a general carbon-free fuel to cover all fuel needs.
A dramatic shift has now occurred, in which the problems of global warming and climate change are now acknowledged and efforts are being made to solve them. Therefore, it is very encouraging that some of the world""s biggest petroleum companies now state that they want to help solve these problems. A number of American utilities vow to find ways to reduce the harm done to the atmosphere by their power plants. DuPont, the world""s biggest chemicals firm, even declared that it would voluntarily reduce its emissions of greenhouse gases to 35% of their level in 1990 within a decade. The automotive industry, which is a substantial contributor to emissions of greenhouse gases and other pollutants (despite its vehicular specific reductions in emissions), has now realized that change is necessary as evidenced by their electric and hybrid vehicles.
Hydrogen is the xe2x80x9cultimate fuel.xe2x80x9d In fact, it is considered to be xe2x80x9cTHExe2x80x9d fuel for the future. Hydrogen is the most plentiful element in the universe (over 95%). Hydrogen can provide an inexhaustible, clean source of energy for our planet which can be produced by various processes. Utilizing the inventions of subject assignee, the hydrogen can be stored and transported in solid state form in trucks, trains, boats, barges, etc. (see the ""810 and ""497 applications). For instance, a truck carrying 15 tons of hydride material, will contain 1050 Kg (assuming 7 wt % storage) of hydrogen, which is 412,000 standard cubic feet of hydrogen. This is enough fuel to supply 175 cars at 6 Kg/car. Assuming 1 ton of hydride occupies a volume of 1 cubic meter, and adding an additional 33% volume for cooling, the truck to carry the material will need to be about 20,000 liters in volume.
A fuel cell is an energy-conversion device that directly converts the energy of a supplied gas into an electric energy. Researchers have been actively studying fuel cells to utilize the fuel cell""s potential high energy-generation efficiency. The base unit of the fuel cell is a cell having a cathode, an anode, and an appropriate electrolyte. Fuel cells have many potential applications such as supplying power for transportation vehicles, replacing steam turbines and power supply applications of all sorts. Despite their seeming simplicity, many problems have prevented the widespread usage of fuel cells.
Presently most of the fuel cell R and D focus is on P.E.M. (Proton Exchange Membrane) fuel cells. The P.E.M. fuel cell suffers from relatively low conversion efficiency and has many other disadvantages. For instance, the electrolyte for the system is acidic. Thus, noble metal catalysts are the only useful active materials for the electrodes of the system. Unfortunately, not only are the noble metals costly, they are also susceptible to poisoning by many gases, and specifically carbon monoxide (CO). Also, because of the acidic nature of the P.E.M fuel cell, the remainder of the materials of construction of the fuel cell need to be compatible with such an environment, which again adds top the cost thereof. The proton exchange membrane itself is quite expensive, and because of it""s low conductivity at temperatures below 80xc2x0 C., inherently limits the power performance and operational temperature range of the P.E.M. fuel cell (the PEM is nearly non-functional at low temperatures, unlike the fuel cell of the instant invention). Also, the membrane is sensitive to high temperatures, and begins to soften at 120xc2x0 C. The membrane""s conductivity depends on water and dries out at higher temperatures, thus causing cell failure. Therefore, there are many disadvantages to the P.E.M. fuel cell which make it somewhat undesirable for commercial/consumer use.
The conventional alkaline fuel cell has some advantages over P.E.M. fuels cells in that they have higher operating efficiencies, they use less expensive materials of construction, and they have no need for expensive membranes. The alkaline fuel cell also has relatively higher ionic conductivity in the electrolyte, therefore it has a much higher power capability. While the conventional alkaline fuel cell is less sensitive to temperature than the PEM fuel cell, the platinum active materials of conventional alkaline fuel cell electrodes become very inefficient at low temperatures. Unfortunately, conventional alkaline fuel cells still suffer from certain disadvantages. For instance, conventional alkaline fuel cells still use expensive noble metals catalysts in both electrodes, which, as in the P.E.M. fuel cell, are susceptible to gaseous contaminant poisoning. The conventional alkaline fuel cell is also susceptible to the formation of carbonates from CO2 produced by oxidation of the anode carbon substrates or introduced via impurities in the fuel and air used at the electrodes. This carbonate formation clogs the electrolyte/electrode surface and reduces/eliminates the activity thereof. The invention described herein eliminates this problem from the anode.
Fuel cells, like batteries, operate by utilizing electrochemical reactions. Unlike a battery, in which chemical energy is stored within the cell, fuel cells generally are supplied with reactants from outside the cell. Barring failure of the electrodes, as long as the fuel, preferably hydrogen, and oxidant, typically air or oxygen, are supplied and the reaction products are removed, the cell continues to operate.
Fuel cells offer a number of important advantages over internal combustion engine or generator systems. These include relatively high efficiency, environmentally clean operation especially when utilizing hydrogen as a fuel, high reliability, few moving parts, and quiet operation. Fuel cells potentially are more efficient than other conventional power sources based upon the Carnot cycle.
The major components of a typical fuel cell are the anode for hydrogen oxidation and the cathode for oxygen reduction, both being positioned in a cell containing an electrolyte (such as an alkaline electrolytic solution). Typically, the reactants, such as hydrogen and oxygen, are respectively fed through a porous anode and cathode and brought into surface contact with the electrolytic solution. The particular materials utilized for the cathode and anode are important since they must act as efficient catalysts for the reactions taking place.
In an alkaline fuel cell, the reaction at the anode occurs between the hydrogen fuel and hydroxyl ions (OHxe2x88x92) present in the electrolyte, which react to form water and release electrons:
H2+2OHxe2x88x92xe2x86x922H2O+2exe2x88x92.
At the cathode, the oxygen, water, and electrons react in the presence of the cathode catalyst to reduce the oxygen and form hydroxyl ions (OHxe2x88x92):
O2+2H2O+4exe2x88x92xe2x86x924OHxe2x88x92.
The flow of electrons is utilized to provide electrical energy for a load externally connected to the anode and cathode.
It should be noted that the anode catalyst of the alkaline fuel cell is required to do more than catalyze the reaction of H+ ions with OHxe2x88x92 ions to produce water. Initially the anode must catalyze and accelerate the formation of H+ ions and exe2x88x92 from H2. This occurs via formation of atomic hydrogen from molecular hydrogen. The overall reaction can be seen as (where M is the catalyst): M+H2xe2x86x922MHxe2x86x92M+2H++2exe2x88x92. Thus the anode catalyst must not only efficiently catalyze the formation of water at the electrolyte interface but must also efficiently dissociate molecular hydrogen into ionic hydrogen. Using conventional anode material, the dissociated hydrogen is transitional and the hydrogen atoms can easily recombine to form hydrogen if they are not used very quickly in the oxidation reaction. Withe the hydrogen storage anode materials of the inventive instant startup fuel cells, hydrogen is trapped in hydride form as soon as they are created, and then are used as needed to provide power.
In addition to being catalytically efficient on both interfaces, the catalytic material must be resistant to corrosion by the alkaline electrolyte. Without such corrosion resistance, the electrode would quickly succumb to the harsh environment and the cell would quickly lose efficiency and die.
One prior art fuel cell anode catalyst is platinum. Platinum, despite its good catalytic properties, is not very suitable for wide scale commercial use as a catalyst for fuel cell anodes, because of its very high cost. Also, noble metal catalysts like platinum, also cannot withstand contamination by impurities normally contained in the hydrogen fuel stream. These impurities can include carbon monoxide which may be present in hydrogen fuel or contaminants contained in the electrolyte such as the impurities normally contained in untreated water including calcium, magnesium, iron, and copper.
The above contaminants can cause what is commonly referred to as a xe2x80x9cpoisoningxe2x80x9d effect. Poisoning occurs where the catalytically active sites of the material become blackened and inactivated by poisonous species invariably contained in the fuel cell. Once the catalytically active sites are inactivated, they are no longer available for acting as catalysts for efficient hydrogen oxidation reaction at the anode. The catalytic efficiency of the anode therefore is reduced since the overall number of available catalytically active sites is significantly lowered by poisoning. In addition, the decrease in catalytic activity results in increased over-voltage at the anode and hence the cell is much less efficient adding significantly to the operating costs. Over-voltage is the difference between the electrode potential and it""s equilibrium value, the physical meaning of over-voltage is the voltage required to overcome the resistance to the passage of current at the surface of the anode (charge transfer resistance). The over-voltage represents an undesirable energy loss which adds to the operating costs of the fuel cell.
In related work, U.S. Pat. No. 4,623,597 (xe2x80x9cthe ""597 patentxe2x80x9d) and others in it""s lineage, the disclosure of which is hereby incorporated by reference, one of the present inventors, Stanford R. Ovshinsky, described disordered multi-component hydrogen storage materials for use as negative electrodes in electrochemical cells for the first time. In this patent, Ovshinsky describes how disordered materials can be tailor made (i.e., atomically engineered) to greatly increase hydrogen storage and reversibility characteristics. Such disordered materials are amorphous, microcrystalline, intermediate range order, and/or polycrystalline (lacking long range compositional order) wherein the polycrystalline material includes topological, compositional, translational, and positional modification and disorder. The framework of active materials of these disordered materials consist of a host matrix of one or more elements and modifiers incorporated into this host matrix. The modifiers enhance the disorder of the resulting materials and thus create a greater number and spectrum of catalytically active sites and hydrogen storage sites.
The disordered electrode materials of the ""597 patent were formed from lightweight, low cost elements by any number of techniques, which assured formation of primarily non-equilibrium metastable phases resulting in the high energy and power densities and low cost. The resulting low cost, high energy density disordered material allowed the batteries to be utilized most advantageously as secondary batteries, but also as primary batteries.
Tailoring of the local structural and chemical order of the materials of the ""597 patent was of great importance to achieve the desired characteristics. The improved characteristics of the anodes of the ""597 patent were accomplished by manipulating the local chemical order and hence the local structural order by the incorporation of selected modifier elements into a host matrix to create a desired disordered material. Disorder permits degrees of freedom, both of type and of number, within a material, which are unavailable in conventional materials. These degrees of freedom dramatically change a materials physical, structural, chemical and electronic environment. The disordered material of the ""597 patent have desired electronic configurations which result in a large number of active sites. The nature and number of storage sites were designed independently from the catalytically active sites.
Multiorbital modifiers, for example transition elements, provided a greatly increased number of storage sites due to various bonding configurations available, thus resulting in an increase in energy density. The technique of modification especially provides non-equilibrium materials having varying degrees of disorder provided unique bonding configurations, orbital overlap and hence a spectrum of bonding sites. Due to the different degrees of orbital overlap and the disordered structure, an insignificant amount of structural rearrangement occurs during charge/discharge cycles or rest periods therebetween resulting in long cycle and shelf life.
The improved battery of the ""597 patent included electrode materials having tailor-made local chemical environments which were designed to yield high electrochemical charging and discharging efficiency and high electrical charge output. The manipulation of the local chemical environment of the materials was made possible by utilization of a host matrix which could, in accordance with the ""597 patent, be chemically modified with other elements to create a greatly increased density of electro-catalytically active sites and hydrogen storage sites.
The disordered materials of the ""597 patent were designed to have unusual electronic configurations, which resulted from the varying 3-dimensional interactions of constituent atoms and their various orbitals. The disorder came from compositional, positional and translational relationships of atoms. Selected elements were utilized to further modify the disorder by their interaction with these orbitals so as to create the desired local chemical environments.
The internal topology that was generated by these configurations also allowed for selective diffusion of atoms and ions. The invention that was described in the ""597 patent made these materials ideal for the specified use since one could independently control the type and number of catalytically active and storage sites. All of the aforementioned properties made not only an important quantitative difference, but qualitatively changed the materials so that unique new materials ensued.
Disorder can be of an atomic nature in the form of compositional or configurational disorder provided throughout the bulk of the material or in numerous regions of the material. The disorder also can be introduced by creating microscopic phases within the material which mimic the compositional or configurational disorder at the atomic level by virtue of the relationship of one phase to another. For example, disordered materials can be created by introducing microscopic regions of a different kind or kinds of crystalline phases, or by introducing regions of an amorphous phase or phases, or by introducing regions of an amorphous phase or phases in addition to regions of a crystalline phase or phases. The interfaces between these various phases can provide surfaces which are rich in local chemical environments which provide numerous desirable sites for electrochemical hydrogen storage.
These same principles can be applied within a single structural phase. For example, compositional disorder is introduced into the material which can radically alter the material in a planned manner to achieve important improved and unique results, using the Ovshinsky principles of disorder on an atomic or microscopic scale.
One attempt at improving the electrode material for fuel cells is embodied in U.S. Pat. No. 5,795,669 to Wilkinson, et al. Therein is disclosed a composite electrode material including two catalyst materials. One of the materials contains an active gas phase catalyst, and the other material contains an active electrochemical catalyst. Unfortunately, none of the described materials store hydrogen, and as such, are not useful as a built in initialization supply of hydrogen for the fuel cell.
Until now no one but Ovshinsky (in U.S. Pat. No. 4,487,818, the disclosure of which is incorporated herein by reference) has employed the Ovshinsky principles of atomic engineering to tailor materials which uniquely and dramatically advance the fuel cell art. Specifically there is a need for materials which allow fuel cells to operate in a wide range of temperatures that such a fuel cell will be exposed to under ordinary consumer use. There is also a need for materials which allow the fuel cell to be run in reverse as an electrolyzer to utilize/store recaptured energy. Finally there is a need in the art for materials which allow the fuel cell to startup instantaneously by providing an internal source of fuel. One of the needed materials is an inexpensive hydrogen storage anode material which is highly catalytic to the dissociation of molecular hydrogen and the formation of water from hydrogen and hydroxyl ions as well as being corrosion resistant to the electrolyte, resistant to contaminant poisoning from the reactant stream and capable of working in a wide temperature range. Also needed is a non-noble metal catalytic material to be used in conjunction with the hydrogen storage materials of the instant invention to enhance the dissociation of hydrogen and the oxidation of hydrogen.
The object of the instant invention is a hydrogen storage composite material which employs both: 1) a hydrogen storage alloy which has excellent catalytic activity for the formation of atomic hydrogen from molecular hydrogen, outstanding catalytic activity toward the formation of water from hydrogen ions and hydroxyl ions, and has exceptional corrosion resistance toward the alkaline electrolyte of an alkaline fuel cell; as well as 2) an additional catalytic material which enhances the dissociation of molecular hydrogen into atomic hydrogen and/or the formation of water molecules from hydrogen ions and hydroxyl ions.
The catalytic materials are formed from non-equilibrium metastable highly disordered materials formed by modification techniques. The technique of modification to provide a non-equilibrium material having a high degree of disorder provides unique bonding configurations, orbital overlap and hence a spectrum of catalytically active sites for the hydrogen oxidation reaction. The modification technique involves tailoring of the local structural and chemical order of the materials of the present invention and is of great importance to achieve the desired characteristics. Amorphous materials having only short range order can be utilized as can crystalline materials having long range order, but where the structure is deliberately modified to increase the density of catalytically active sites above that obtainable in the prior art.
The improved catalytic activity is accomplished by manipulating the local chemical order and hence the local structural order by the incorporation of selected modifier elements into a selected host matrix to create the desired disordered material. The disordered multicomponent materials may be amorphous, polycrystalline (but lacking long range order) or microcrystalline in structure, or an intimate mixture of amorphous and polycrystalline or microcrystalline phases.
The tailor-made materials include a host matrix including at least one transition element, and at least one modifier element introduced into the host matrix in a non-equilibrium manner. The incorporation of the modifier element or elements in this manner provides the desired disordered structure of the material and creates numerous local structural and chemical environments which act as catalytically active sites for the hydrogen oxidation reaction in a fuel cell anode. Nickel is an example of a transition element particularly suitable for forming the host matrix. A few examples of the preferred modifier elements include transition elements such as Ti, V, Mo, and Zr and other elements such as Mg, Si, or Al. The most useful alloys are the Nixe2x80x94Tixe2x80x94Mo alloys.
A second object of the instant invention is the use of the composite hydrogen storage materials as the anode material of a fuel cell which has the ability to start up instantly and can accept recaptured energy such as that of regenerative braking by operating in reverse as an electrolyzer. The instant startup fuel cells have increased efficiency and power availability (higher voltage and current) and a dramatic improvement in operating temperature range (xe2x88x9220 to 150xc2x0 C.) The fuel cell employs a composite anode active material which includes materials with hydrogen storage capacity and non-storage catalytically active materials. The anode material is low cost, containing no noble metals. The anode materials are robust and poison resistant. The anode materials are is easy to produce, by proven low cost production techniques. The anode eliminates the use of carbon therein, thus helping to eliminating the carbonate poisoning of the fuel cell.
The hydrogen storage alloys useful in the anodes of the instant startup fuel cells reversibly absorb and release hydrogen and have a fast hydrogenation reaction rate and a long shelf-life. The hydrogen storage alloy is preferably selected from Rare-earth/Misch metal alloys, zirconium alloys, titanium alloys and mixtures or alloys thereof. The preferred hydrogen storage alloy contains enriched catalytic nickel regions distributed throughout the oxide surface of the particulate thereof. The catalytic nickel regions are 50-70 Angstroms in diameter and vary in proximity from 2-300 Angstroms (preferably from 50-100 Angstroms). An example of such an alloy has the following composition:
(Base Alloy)aCobMncFedSne 
where the Base Alloy comprises 0.1 to 60 atomic percent Ti, 0.1 to 40 atomic percent Zr, 0 to 60 atomic percent V, 0.1 to 57 atomic percent Ni, and 0 to 56 atomic percent Cr; b is 0 to 7.5 atomic percent; c is 13 to 17 atomic percent; d is 0 to 3.5 atomic percent; e is 0 to 1.5 atomic percent; and a+b+c+d+e=100 atomic percent.